Analysis of microbial populations associated with a sorghum-based fermented product used as an infant weaning cereal.

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Abstract

The incidences of diarrhoeal episodes in infants and children have mostly been associated with
the consumption of contaminated weaning foods. This is especially true in developing
countries where factors such as the lack of sanitation systems and electricity have been found
to contribute to an increase in the incidence of microbiologically contaminated weaning foods.
The process of fermentation has been found to reduce the amount of microbiological
contamination in such foods as a result of the production of antimicrobial compounds such as
organic acids, peroxides, carbon dioxide and bacteriocins. In this study, microbiological
surveys were conducted on sorghum powder samples and their corresponding fermented and
cooked fermented porridge samples collected from an informal settlement of the Gauteng
Province of South Africa. The process of fermentation was found to result in significant
decreases (P>0.05) in Gram-negative counts and spore counts, while aerobic plate counts
decreased slightly. Lactic acid bacteria counts, however, increased significantly (P>0.05). The
cooking process was found to result in further significant decreases (P>0.05) in all counts.
Sorghum powder samples and fermented porridge samples were found to be contaminated
with potential foodborne pathogens, including Bacillus cereus, Clostridium perfringens and
Escherichia coli, however, none of the pathogens tested for were detected in any of the cooked
fermented porridge samples. SDS-PAGE and phenotypic analysis of 180 lactic acid bacteria
isolated from sorghum powder samples and their corresponding fermented and cooked
fermented porridge samples showed that a majority of the isolates were lactobacilli and
leuconostocs, however, some isolates were identified as pediococci and lactococci. These
results demonstrated the heterogeneity of the lactic acid bacteria isolates that were associated
with fermentation processes in this study. Of the lactic acid bacteria identified, Lactobacillus
plantarum and Leuconostoc mesenteroides strains were found to have the highest distribution
frequencies, being distributed in 87% and 73% of the households, respectively. Analysis of
Lactobacillus plantarum (58) and Leuconostoc mesenteroides (46) strains isolated from
sorghum powder samples and corresponding fermented and cooked fermented porridge
samples by AFLP fingerprinting showed that they originated from a common source, which
was sorghum powder. There was, however, evidence of strains that may have been introduced
at household level. Antimicrobial activity of selected lactic acid bacteria was found to be
mainly due to a decrease in pH in fermented and cooked fermented porridge samples. None
of the lactic acid bacteria tested seemed to produce bacteriocins.